Unhealthy obsessions?

Anyone have an interest which others find dubious? I have a couple I think, but mostly I've just had a fascination with Jack the Ripper. I don't derive any inappropriate pleasure out of the materials I read or research, just an interest in the various theories as to who the Ripper really was, the public reaction, and how forensics of the day worked or didn't work. On the forensics, I think how primitive some of their techniques were, and how cases gone cold then would be easier to solve nowadays.

I confess that looking at the sociopathic mind in all its horror also is intriguing, and as a writer, insight into that kind of a mind is invaluable to some characters.

What other kinds of unhealthy obsessions do people have? At least those that can be talked about. ;)